Neurons that synthesize the peptide neurotensin (NT) are particularly abundant in the preoptic area and may play an important role in regulating neuroendocrine function, many aspects of which are sexually differentiated. This proposal seeks to clarify the relationship between female-specific, estrogen-dependent expression of the neurotensin/neuromedin N (NT/N) gene in the rat preoptic area and female-specific regulation of luteinizing hormone (LH) secretion. A major objective of this proposal is to determine the extent to which estrogen can act directly on NT neurons in the preoptic area. To that end, in situ hybridization histochemistry will be used to determine the detailed regional distribution of neurons that express both NT/N mRNA and estrogen receptor mRNA in the male preoptic area and female preoptic area. A second major objective of this proposal is to determine the extent to which NT can act directly on neurons that synthesize gonadotropin-releasing hormone (GnRH). To that end, in situ hybridization histochemistry will be used to determine the detailed regional distribution of neurons that express both GnRH mRNA and NT receptor mRNA in the basal forebrain of the male and female. In addition, the effect of estrogen on the abundance of NT receptor mRNA in GnRH neurons will be determined. A third major objective of this proposal is to investigate the development of female-specific NT/N gene expression in the preoptic area. Developmental parameters to be investigated include: a) the age at which the distribution of NT/N mRNA in the preoptic area becomes sexually differentiated, b) the extent to which sexually differentiated expression of NT/N mRNA in the adult preoptic area is determined by neonatal androgen levels, and c) the age at which estrogen is able to alter the abundance of NT/N mRNA in the female preoptic area. The results of these developmental studies will help to clarify the role of NT neurons in the development of female-specific regulation of LH secretion. Identifying neuro- transmitters that regulate GnRH neurons will further our understanding of neural regulation of the menstrual cycle, may provide insight into its pathology, and may point the way toward novel therapeutic approaches.